External Triggers

What it is

Before a habit exists, something has to prompt the first several visits, and that something is external. Eyal's four-type taxonomy, set out in Hooked (2014), sorts external triggers by who pays for them and how often they can plausibly recur.

Paid triggers, advertising and sponsored placement, get someone in the door, but they're expensive per acquisition and stop the moment the spending stops. Earned triggers, a mention in the press, a spot in an app store's featured list, are free but not repeatable on demand; a product can't simply decide to earn coverage again next week. Relationship triggers borrow another person's attention to do the prompting, an invite, a notification framed as coming from a contact, a friend's activity showing up in a feed. They're powerful because they read as personal rather than commercial, but a product cannot fire one on its own; it needs a person willing to be the vehicle.

Owned triggers are the exception to all of this. Once a person has installed an app, subscribed to a list or enabled a notification, the product can prompt them again at close to zero marginal cost, as often as it likes, without paying for placement or waiting for a journalist or borrowing a friend's credibility. That is the economic reason owned triggers are the only type that can plausibly carry someone from a single visit to a standing habit: they're the only kind cheap enough to repeat until repetition itself becomes the pattern.

Relationship triggers deserve particular scrutiny, because they are the type most easily disguised. A notification that reads "so-and-so tagged you" or "your friend just joined" is, formally, an owned trigger firing on the product's own schedule; what makes it a relationship trigger is that it borrows the appearance of a human being reaching out. That borrowed authenticity is exactly what makes it effective, and exactly what makes it easy to abuse: the person reading it experiences a prompt from a friend, when the actual author of the prompt is the product deciding when to send it.

External triggers sit at the entry point of the wider Hook Model: they open the loop, and the model's own argument is that they are meant to become unnecessary. As a product accumulates enough completed cycles, the trigger that once had to arrive from outside starts to arrive from inside instead, typically as an uncomfortable feeling the person has learned a specific action will relieve.

In effect

Coca-Cola's "Thirsty?" vending machine

Eyal describes a Coca-Cola vending machine fitted with a thermometer, which prompts a purchase message the moment the temperature crosses a threshold that makes a cold drink most appealing (p.41). It is a paid, environmental trigger firing at the point of maximum receptivity, a low-tech version of the same principle that governs when a notification gets sent: not just that a cue arrives, but that it arrives when the person is already primed to act on it.

Apple's 7.4 trillion notifications

By Eyal's later account in Indistractable (2019), Apple's devices sent 7.4 trillion push notifications in 2013, and Adam Marchick of the notification platform Kahuna estimated that under 15 per cent of users ever change a notification setting. That gap, between how many owned triggers a person's devices fire and how rarely they intervene on the default, is what makes owned triggers the workhorse of the whole system: most people simply absorb whatever cadence the product has set.

PayPal's relationship-trigger loop

In its early growth, PayPal paid users a referral bonus to send money to friends, and the recipient had to create an account to receive it (pp.45–46). The trigger arriving in the recipient's inbox came from a real acquaintance, not from PayPal, which is precisely why it converted so well: one person's ordinary action became another person's personal prompt, at a cost PayPal could scale far beyond what a paid advertisement could have bought at the same price.

What it does not say

The four-type taxonomy is a design framework, not a tested causal model with effect sizes attached; there is no controlled comparison establishing that owned triggers convert at some measured rate above paid or earned ones across products in general, only case studies in which they appear to have worked. Eyal himself resists treating every external trigger as harmful, citing SMS-based smoking-cessation programmes as an external trigger used for a purpose the recipient endorses. The relevant question, which the framework itself supplies, is not whether a trigger is external but who it is serving.

Who developed it

Nir Eyal set out the four-type taxonomy of external triggers in Hooked (2014) as the entry point of the Hook Model.

---